Electrolytic capacitors are often formed from valve action materials that are capable of being oxidized to form a dielectric layer. Typical valve action metals are niobium and tantalum. More recently, capacitors have been developed that employ an anode made from an electrically conductive oxide of niobium and a niobium pentoxide dielectric. Niobium oxide based capacitors have significant advantages over tantalum capacitors. For example, niobium oxide is more widely available and potentially less expensive to process than tantalum. Niobium oxide capacitors are also more stable against further oxidation and thus less prone to thermal runaway when over-voltaged (or otherwise over-loaded) than tantalum and niobium. Further, niobium oxide has several orders of magnitude lower minimum ignition energy compared to niobium and tantalum. Niobium oxide capacitors may also have a unique high resistance failure mechanism that limits the leakage current to a level below the capacitor's thermal runaway point. In niobium oxide capacitors, for instance, a passive crystallic NbO2 or Nb2O5 film may form upon contact with the atmosphere after sintering of the NbO anode. Such passive films or other impurities can act as a nucleus and give rise to more conductive crystallic Nb2O5 in the subsequent anodically grown dielectric film. This may lead to leakage current instability at accelerated temperature and voltage load.
As such, a need currently exists for an electrolytic capacitor anode having a reduced number of defects in the dielectric layer.